[time-nuts] The best GPSDO ?

[SAIDJACK at aol.com]

Ulrich,
 
that depends on how good the particular unit is you happen to get your  
hands on. TVB shows a more than 10x variation in performance on his  many 
Z3801A units for example.
 
I recently got, and discussed on this list a 58503A unit from China  
(modified Z3805A with 10811 Double Oven) which I find to be the best GPSDO I  have 
ever tested (and I have tested a lot over the last 5+ years), and it's only 
 a 6-channel unit.
 
In fact the only way I can test it's performance is to use a Wenzel  
Sprinter with -172dBc noise floor for phase noise, and a BVA 8600 for ADEV  
testing. But even then the unit's ADEV outperforms the BVA above a couple of 100  
seconds, and I don't know if the ADEV floor I am measuring is my BVA or the  
Z3805. It reports 800ns predicted drift over 24 hours. Others have  
indicated that their Z380x units can achieve even better than that. On the  phase 
noise plot, you will notice the Time Pod indicates we are measuring at  it's 
noise floor between ~10Hz and ~400Hz.
 
Attached are those two PN and ADEV plots. You will note that this unit is  
still out-performed by some of the Z3801A units that TVB tested, wish I had 
one  of those.
 
So this Z3805A has the best ADEV AND Phase Noise that I have seen in one  
single unit. Other GPSDO units I have tested may have better phase noise and  
less spurs, OR better ADEV, but not both in one unit.
 
BTW: I would stay away from the Z3815A's they have quite bad spurs and  
phase noise performance, and all the ones I have seen have jumping  crystals.
 
The Thunderbolts I have seen have 2x to 3x or worse ADEV, and at least 5dB  
worse phase noise, and many more spurs.
 
So in summary, the question is probably not who makes the best GPSDO, the  
question is how do you get your hands on the best particular sample  unit 
out there.. and then how do you get the best reference  oscillator for phase 
noise, and one for ADEV measurements.
 
bye,
Said
 
 
In a message dated 9/28/2012 01:19:23 Pacific Daylight Time,  
df6jb at ulrich-bangert.de writes:

Gentlemen,

I know that lots of you own a GPSDO, some of you  two or even more. For that
reason I conclude that there must be a lot of  knowledge available on how
different GPSDOs perform against each other.  This is why I want to put
forward the question for the BEST GPSDO in terms  of

a) phase noise up to 100 kHz from the carrier

b) AD for tau  > 0.1 s and < say 7200 s (where the AD is controlled by LO 
AND
GPS  and not by GPS alone)


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